This invention is concerned with compositions useful in the molding and curing of automobile tire carcasses and similar hollow rubber articles and is directed particularly at compositions useful to prevent adhesion of the interior of the tire carcass to the pressure bag used in conjunction with the mold.
In the manufacture of automobile tires, uncured rubber is compounded with a variety of agents built into a carcass with desired reinforcing fabric, synthetic fibers, fiber glass roving or metal strands in various configurations. The raw carcass is then cured in a mold; the inside of the raw carcass must be coated with a release film to prevent adhesion of the carcass to the pressure bag during the curing operation, conducted at fairly high temperatures with the carcass under pressure. During the curing operation, an air bag is placed inside the carcass and is inflated to apply the desired pressure to force the carcass into intimate contact with the mold which corresponds to the tread to be imparted to the finished tire. It is necessary that a film of some material be placed between the interior of the raw carcass and the air bag to prevent adhesion of the carcass interior to the air bag. This has been done in the past by spraying the inside surface of the tire carcass with a release coating comprising a dispersion of mica in a silicone containing formulation. Because of the raw materials used, these coatings are expensive and they have two major disadvantages. The first and most objectionable problem with these release coatings which contain silicone is that, where the carcass needs some repair after curing, it is extremely difficult to apply more compound over the interior surface and get adequate adhesion. It is necessary to first completely dissolve away the release coating-- time-consuming, expensive operation. The second problem is that the pressure bags accumulate deposits which build up, so that they must be cleaned after a certain number of molding cycles. This invention aims to overcome both the repair and build-up problems connected with silicone release coatings, while at the same time providing good release at substantial cost savings.